This invention relates to earth excavation machines, and, more particularly to tunnel boring machines for excavation of mine entry tunnels and haulage ways in hard rock.
A primary object of the present invention is to provide a tunnel boring machine for excavating a tunnel of generally rectangular cross-sectional configuration. The tunnel has straight sidewalls and a slightly elliptical floor and roof. The width of the excavation is nominally twice the height, but this ratio can be varied slightly to suit specific needs.
It is common mining practice to bore a series of parallel tunnels, generally referred to as "drifts", for extracting minerals in a layer of earth strata. The area between parallel drifts are referred to as columns and provide vertical support to the overlaying strata.
An important feature of the excavation shape produced by the machine of the present invention is the column or wall configuration left between parallel drifts. The elliptical fillets in the column corners which are created by this smooth wall boring machine produce minimum ground disturbance thus providing very low rock stress in the areas of the columns. This allows the thickness of the columns to be decreased providing a higher mineral extraction ratio.
For a typical 121/2 ft. high.times.25 ft. wide tunnel entry, the cutterwheel of the machine would be 25 ft. in diameter and approximately 9 ft. tall. The cutterwheel would be oriented with its axis of rotation 10 to 15 degrees from vertical. Large rolling disc cutters which are common in tunnelling and raise boring, would be mounted on the rim and upper surface of the cutterwheel. The slight 10.degree.-15.degree. inclination of the cutterwheel produces the elliptical shape of the floor and roof and facilitates muck pickup under the raised back portion of the cutterwheel.
The rotating cutterwheel is urged against the rock face by longitudinal thrust cylinders. As the rotating cutterwheel is thrust into the rock face, rock between cutter discs is spalled free of the rock mass and falls to the drift floor where it is gathered by the cutterwheel paddles and deposited on a machine belt conveyor for subsequent deposit into the mine haulage system.
A feature of the machine is its ability to continually thrust the cutterwheel into the rock so that there is no time lost during a grip and reset cycle as is common with tunnel boring machines. With this feature, machine utilization rates of 75-80% can be achieved instead of 50-60% which is common with machines that must reset.
The machine advances by alternately clamping into the side walls (or the roof and floor if desired) with two sets of gripper assemblies mounted transversely relative the thrust cylinders. While the front set is gripping the rear set is resetting, then the rear set grips and the front resets thereby continually allowing the machine to thrust forward.
Each set of gripper assemblies comprises two coaxial piston arms which are independently operable and extend in opposite directions to engage opposite walls of the tunnel. By extending one piston arm a greater distance than the other associated piston arm, the machine may be moved laterally, thus providing a steering means.
A machine needed to bore a 121/2 ft..times.25 ft. drift in oil shale of 14,000 psi may weigh approximately 400 to 500 tons. The machine would require on the order of 1200-1400 horsepower to rotate the cutterwheel and on the order of 1,000,000 pounds of thrust to thrust the cutterwheel forward into the rock face.